The present invention relates to double-band press for the continuous production of wood-chip boards and similar board materials.
The wood particles are flat chips, as well as other particles produced by the reduction of wood, e.g., by planing, chopping, sawing, grinding, or disintegration (Zerfasern--Tr.) that are combined with a binding agent in the form of a thermal hardening plastic resin and scattered or spread so as to form a mat or a fleece. The mat is compressed between the surfaces to form a panel-like or similar shaped part, whereby the surfaces are heated and heat flows from the surfaces into the mat so as to increase the temperature, harden the bonding agent, and consolidate the mat to form a compact panel or the like. In a multi-stage press the "surfaces" are the pressure panels or plates and in a double-band press they are both the bands. In place of flat surfaces, as in the cases quoted above, presses with a large drum and a steel band that passes around this are used to produce thin panels.
During the production of wood-chip panels and similar materials, the pressure and temperature curves at the initial phase of compression are extremely important for the properties of the finished panel. In conventional continuous presses, this compression takes place in the area of the feed gap of the supporting structure, and it is already known that the feed gap can be made adjustable and the adjustment can be controlled depending on the type of production (DE-PS 31 33 792, DE-AS 23 43 427) in order that the formation of the panel characteristics can be influenced in an appropriate manner.
The plastification that the wood fibres or chips undergo during the combined effect of pressure, heat, and the moisture which is present in the mat, which is carefully controlled, plays a very important part in the way that the product turns out.
DE-OS 35 38 531, which deals with the so-called calendering press of this kind, with a heated pressure drum that is enclosed about a portion of its periphery by a steel band that passes over guide and pressure rollers, describes the fleece at the start of the compression gap is compressed to a value that lies in the range above or below the normal thickness of the finished panel and is then heated while contained between heated pressure drums and the steel band during simultaneous forward movement until such time as the particles enter their plastic state and the bonding agent has been brought to the required hardening temperature. These measures are intended to achieve a good panel surface during a single pressing operation and at the same time achieve better thermal transfer in the layer of chips because of the increased density at the start of the compression, as well as a more rapid penetration of the heat into the outer areas of the compressed chip layer. DE-OS 35 38 531 does not provide details about the management of pressure and temperature.
It is the task of the present invention to so configure this type of process and the appropriate pressing such that in particular the surface quality of the wood chip and similar panels produced thereby is enhanced, so that they can be used in the furniture industry without any surface smoothing possibly for the rear walls of cabinets and the bottoms of drawers, and are also suitable for lacquering, and as a basis for laminates.